Brush gear mechanisms are used extensively in certain motors, generators and other rotating electrical machinery to conduct current between stationary and rotating parts (commutators or slip rings). To avoid or at best minimise the wear of the rotating parts, which are typically constructed of copper or brass, brushes are made of soft materials, such as carbon and graphite, so as to preferentially wear. It is important that brush wear is monitored to ensure that the brushes do not wear beyond a minimum level as a completely worn brush can lead to electrical arcing resulting in machine part failure.
There are a number of techniques and methods known for the measurement and determination of brush wear. One such technique involves the closing of a switch, by flags or projections located on the brush, by movement resulting from the brush wear. An example is provided in the German Patent No. DE 34 17 711 A1. Another example is provided in German Patent No. DE 86 00 934 U1. A problem with brush wear monitoring methods utilising brush flag switches is that dust created by the wearing of brush creates a dirty environment in the brush housings in which brush are located. This dust can interfere with the operation and reliability of the switching operation.